Lightning Function Python

Question

I am currently working on writing a function as part of a functions assignment. I am using python 2.7.5 and pygame. We are supposed to write a recursive function that draws lighting. I am currently having an error with my code but I do not know what it is. Here is my code:

from math import *
from pygame import *
from random import *

screen=display.set_mode((800,600))


def lightning(screen,x,y,size,ang):
    if size > 5:
        rang = radians(ang)
        x2 = x-size*cos(rang)
        y2 = y+size*sin(rang)
        draw.line(screen,(200,180,0),(x,y),(x2,y2))
        lightning(screen,x2,y2,size-randint(1,10),ang-randint(-20,10))
        lightning(screen,x2,y2,size-randint(1,10),ang+randint(-10,30))

lightning(screen,400,0,100,randint(60,100))
running=True
while running:
    for evt in event.get():
        if evt.type==QUIT:
            runnning=False
    screen.fill((0,0,0))
    lightning(screen,400,0,100,randint(60,100))
    time.wait(500)

    display.flip()
 quit()

Currently, when I try to add another line of lightning (the "lightning(...)") it does not display any error in the shell and also does not display anything in the pygame window. When I have only one line, the lightning functions properly. I would just like to know where my error is and reasons to why it is causing the error. Any help is appreciated. Thanks.

Maybe because you never actually quit the function? It's just looping and looping again. — aIKid
– aIKid, Commented Feb 23, 2014 at 23:11
I suggest adding print statements inside lightning() and see what it prints while it is running. If you can't see the output while it is running, write the printed statements into a log file and look at that after you run it. — steveha
– steveha, Commented Feb 25, 2014 at 3:33

furas · Accepted Answer · 2014-02-25 12:56:33Z

For size=100 function ligthning() is call 800 000 to 3 500 000 times.

If you add another line of lightning it gives you even 7 000 000 calls.

Maybe You don't see result because it works too long. Try your code for smaller size.

My code to count ligthning() calls.

from math import *
from pygame import *
from random import *

#---------------------------------------------------------------------

def lightning(screen, x, y, size, ang, count):
    if size > 5:
        rang = radians(ang)
        x2 = x-size*cos(rang)
        y2 = y+size*sin(rang)
        draw.line(screen,(200,180,0),(x,y),(x2,y2))
        count = lightning(screen,x2,y2,size-randint(1,10),ang-randint(-20,10), count)
        count = lightning(screen,x2,y2,size-randint(1,10),ang+randint(-10,30), count)
    return count + 1

#---------------------------------------------------------------------

screen = display.set_mode((800,600))

#lightning(screen,400, 0, 100, randint(60,100))

running = True

while running:

    for evt in event.get():
        if evt.type == QUIT:
            running = False
        elif evt.type == KEYDOWN:
            if evt.key == K_ESCAPE:
                running = False

    screen.fill((0,0,0))
    print 'count: ', lightning(screen, 400, 0, 100, randint(60,100), 0)
    display.flip()

    #time.wait(500)

quit()

EDIT:

Theoretically radint(1,10) can always give 1 so you can always have lightning(...,size-1, ...) and for size=100it can give 2**95 calls.

2**95 = 39 614 081 257 132 168 796 771 975 168L

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